Saddle bearing liner for axial piston pump

ABSTRACT

A saddle bearing liner ( 30 ) for a variable displacement axial piston pump ( 10 ) includes two axially-spaced apart bearing surfaces ( 62, 64 ) with an offset central section ( 54 ) integrally joining them. A hollow projection ( 80 ) extends radially from the convex side of the pressure bearing section ( 50 ) and is received with a recess ( 82 ) of the housing ( 12 ) to locate the liner ( 30 ). The liner ( 30 ) has radially extending ledges ( 70, 72 ) which mate with surfaces ( 74, 76 ) of the housing ( 12 ) to inhibit skewing of the bearing liner ( 30 ) relative to the axis of the bearing surfaces ( 62, 64 ). The projection ( 80 ) is hollow and opens to the bearing surface ( 62 ) so that presurrized fluid from the housing ( 12 ) can be injected between the bearing surface ( 62 ) and the mating surface ( 22 ) of the swashblock ( 20 ). The projection ( 80 ) also prevents the liner ( 30 ) from rotating about the bearing surface axis.

CROSS-REFERENCE TO RELATED APPLICATION

This claims the benefit of U.S. Provisional Patent Application No.60/281,913 filed Apr. 5, 2001.

STATEMENT CONCERNING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

The field of the invention is variable flow axial piston pumps, and inparticular, saddle bearings, sometimes referred to as cradle bearings,for such pumps.

DISCUSSION OF THE PRIOR ART

Variable flow axial piston pumps are well-known from patents such asU.S. Pat. Nos. 3,868,889; 4,710,107; 4,581,980; 4,896,583; and5,630,352. As shown in the '583 patent, there are typically twoliner-type sliding bearings between the concave surfaces of the saddleor cradle and the convex surfaces of the swashblock. These two bearingliners are typically pinned or otherwise affixed to either theswashblock or to the saddle. In addition, the bearings are guided by oneor more surfaces which confront the longitudinal edges of each bearingsection.

Typical prior art constructions have therefore included a number ofparts to assemble a bearing liner to the swashblock or saddle, and alsohave required significant machining of the structures confronting thesides of the bearing liners. It is an object of the present invention toaddress these issues.

SUMMARY OF THE INVENTION

The invention provides a saddle bearing liner in which two spaced apartsaddle bearing liner sliding surfaces are provided which are arcuate andhave an outer surface adapted to mate with an arcuate cradle surface ofthe saddle and have an inner surface adapted to mate with an arcuatesurface of the swashblock. The two saddle bearing liner sections arebridged by a central section which is integral with the saddle bearingliner sections. Thereby, both saddle bearing liner surfaces are providedin a single piece.

In a preferred aspect, the central section of a liner of the inventionhas at least one surface which is offset from the adjacent surfaces ofthe bearing sections. The central section, therefore, mates with thesaddle or swashblock to guide the saddle bearing liner so as to preventit from rocking or becoming skewed excessively between the saddle andswashblock surfaces.

In another useful aspect, a liner of the invention has a projectionwhich fits into a recess of the saddle to locate the liner and preventit from turning about its longitudinal axis. The projection, preferably,extends into a recess of the saddle so that the liner is stationaryrelative to the saddle with the sliding surfaces of the liner beingagainst the swashblock. This makes pinning the liner to the saddle or tothe swashblock unnecessary.

In another preferred aspect, the projection can be hollow, defining apassageway which opens to at least one of the sliding surfaces of theliner. The passageway and the projection at its end opposite from thesliding surface is in communication with pressurized fluid provided bysuitable passageways in the saddle. Preferably, the sliding surfacewhich the passageway opens to is on the pressure side of the liner,meaning that it is axially opposite from the pistons of the pump whichare compressing the fluid. Thus, a pressurized film of fluid ismaintained between the sliding surfaces of the bearing liner on at leastthat side of the liner to reduce friction between the liner and theswashblock.

The foregoing and other objects and advantages of the invention willappear in the detailed description which follows. In the description,reference is made to the accompanying drawings which illustrate apreferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an axial piston pump incorporating asaddle bearing liner of the invention;

FIG. 2 is an exploded perspective view of the pump housing, liner, andswashblock, with portions of the housing broken away to show the saddle;

FIG. 3 is a perspective view of the liner from the outer or saddle sidethereof;

FIG. 4 is a plan view of the liner from the inner or swashblock sidethereof;

FIG. 5 is a cross-sectional view from the plane of the line 5—5 of FIG.4;

FIG. 6 is a cross-sectional view from the plane of the line 6—6 of FIG.4;

FIG. 7 is a longitudinal cross-sectional view of the swashblock from theplane of the line 7—7 of FIG. 2; and

FIG. 8 is a radial cross-sectional view of the swashblock from the planeof the line 8—8 of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a variable displacement axial piston pump 10 has ahousing 12 which defines a saddle or cradle 14 that includes two axiallyspaced apart convex surfaces 16 and 18 (FIG. 2). The pump 10 alsoincludes a swashblock 20 which has convex surfaces 22 and 24 that areshaped to conform to the surfaces 16 and 18 with a saddle bearing liner30 of the invention between the concave 16, 18 and convex 22, 24surfaces. The pump 10 also has a number of pistons 32 which are radiallydisposed about pump axis 34 to reciprocate in cylinders 36 when theswashblock 20 is moved off of its center or balanced position byshuttling control pin 38 to one side or the other, either manually orusing a hydraulically operated piston or other device. As is well-known,the pistons 32 have shoes 40 which slide against a flat face 42 of theswashblock 20 and a shoe retainer 44 which maintains the shoes inposition relative to one another and relative to a fulcrum ball 46. Ashaft 48 which is journaled in the housing turns the piston and cylinderassembly, also as is well-known.

Referring to FIGS. 2–6, the liner 30 has two bearing sections 50 and 52which are axially spaced apart relative to the turning axis of theswashblock, which is the same axis as the turning axis of the liner 30,the axis of the concave saddle surfaces 16 and 18 and the axis of theconvex bearing surfaces 22, 24. A central section 54 of the liner 30 isbetween the bearing sections 50 and 52 and is integral therewith. Theliner 30 can be a polymeric material.

Each of the bearing sections 50 and 52 has an outer convex surface 58,60 which mates with the respective surface 16 or 18 and an inner concavesurface 62, 64 mates with the respective convex surface 22, 24 of theswashblock 20. The central section 54 also has an outer convex surface66 and an inner concave surface 68, with the outer surface 66 beingradially offset from the outer surfaces 58 and 60, and the inner surface68 also being offset from the inner surfaces 62, 64. This offsettingcreates radially extending ledges 70 and 72 on the outer surface of theliner 30, which surfaces face shoulder surfaces 74 and 76 which areundercut into the housing 12. Since the surfaces 70, 72, 74, and 76extend in planes which are perpendicular to the turning axis of theliner 30, the fit of these surfaces with one another keeps the liner 30from becoming skewed, also referred to as rocking, between the saddlesurface 16 and 18 and the swashblock 20. The central section 54 also hasa hole 78 through it through which the shaft 48 extends.

Referring particularly to FIGS. 3–6, a projection 80 extends radiallyfrom surface 58 of bearing section 50 and is received in recess 82 inthe saddle surface 16. The projection 80 is hollow, defining a lumen 84which opens to the sliding bearing surface 62 on the inside of the liner30. The capturing of the projection 80 in the recess 82 fixes the liner30 from rotating relative to the housing 12, so all of the slidingoccurs between the liner 30 and the swashblock 20. Thus, surfaces 62 and64 are sliding bearing surfaces and surfaces 58 and 60 are stationarysupport surfaces.

Referring to FIG. 1, hydraulic fluid under pressure is introduced to therecess 82 by appropriate passageways in the housing 12 so that the fluidunder pressure is injected between the surface 62 and the swashblock 20.Referring to FIG. 1 and FIG. 7, the fluid is introduced to an undercutarea of the swashblock 20 between two ridges 23, 25 on which the concavesurface 22 is defined. Thus, a steady supply of oil under pressure ismaintained to provide a film of oil between the surfaces 22 and thesurface 16. The surface 16 and the surfaces 22 are preferably oppositefrom the outlet of the pump (the compression side of the pump) so thatthey are the pressure bearing surfaces, meaning that they react againstthe positive pressure which is generated by the pistons 32 pumping andthe cylinders 36, which pushes the surfaces 22 toward the surface 62. Onthe lower half of the liner, at surface 64, the pistons in this area aredrawing a relative vacuum to draw fluid into the cylinders 36 so theforces compressing the surfaces 22 against surface 62 are much reduced.

A preferred embodiment of the invention has been described inconsiderable detail. Many modifications and variations will be apparentto those skilled in the art. Therefore, the invention should not belimited to the embodiment described, but should be defined by the claimswhich follow.

1. In a variable displacement axial piston pump having a swashblock witha pair of axially spaced apart convex surfaces and a saddle with amating pair of axially spaced apart concave surfaces to receive theswashblock convex surfaces with bearing material between said matingconcave and convex surfaces, the improvement wherein the bearingmaterial between one pair of mating concave and convex surfaces isintegral with the bearing material between the other pair of matingconcave and convex surfaces, a central section of the same material assaid bearing material joins and is integral with the bearing materialwhich is in between said two pairs of mating concave and convexsurfaces, at least one of the inner and outer surfaces of the centralsection is radially offset from the adjacent surfaces of the bearingmaterial which is between said two pairs of mating concave and convexsurfaces, said offset surface is on the outer side of said bearingmaterial and fits within a recess of said saddle and at least one ledgeis defined between said offset surface and an adjacent surface of saidbearing material, said ledge mating with a surface of said saddle toresist skewing of said bearing material relative to an axis of saidconcave surfaces of said saddle.
 2. The improvement of claim 1, whereintwo said ledges are defined, one on each side of said central section ofsaid bearing material.
 3. The improvement of claim 1, wherein at leastone surface of said bearing material includes a projection whichprojects radially from said surface.
 4. The improvement of claim 3,wherein said projection projects from a convex surface of said bearingmaterial.
 5. The improvement of claim 4, wherein said projectionprojects from said convex surface opposite from a concave slidingsurface of said bearing material.
 6. In a variable displacement axialpiston pump having a swashblock with a pair of axially spaced apartconvex surfaces and a saddle with a mating pair of axially spaced apartconcave surfaces to receive the swashblock convex surfaces with bearingmaterial between said mating concave and convex surfaces, theimprovement wherein the bearing material between one pair of matingconcave and convex surfaces is integral with the bearing materialbetween the other pair of mating concave and convex surfaces, at leastone surface of said bearing material includes a hollow projection whichprojects radially from a convex surface of said bearing materialopposite from a concave sliding surface of said bearing material thatreacts against positive pressures generated by said pump.
 7. Theimprovement of claim 6, wherein said projection opens to said slidingreaction surface.
 8. In a variable displacement axial piston pump havinga swashblock with a pair of axially spaced apart convex surfaces and asaddle with a mating pair of axially spaced apart concave surfaces toreceive the swashblock convex surfaces with bearing material betweensaid mating concave and convex surfaces, the improvement wherein thebearing material between one pair of mating concave and convex surfacesis integral with the bearing material between the other pair of matingconcave and convex surfaces, at least one surface of said bearingmaterial includes a hollow projection which projects radially from asurface of said bearing material and opens to a sliding surface of saidbearing material.
 9. In a variable displacement axial piston pump havinga swashblock with a pair of axially spaced apart convex surfaces and asaddle with a mating pair of axially spaced apart concave surfaces toreceive the swashblock convex surfaces with bearing material betweensaid mating concave and convex surfaces, the improvement wherein thebearing material between one pair of mating concave and convex surfacesis integral with the bearing material between the other pair of matingconcave and convex surfaces, at least one surface of said bearingmaterial includes a projection which projects radially from said surfaceand said projection is received within a recess of said saddle therebyfixing the bearing material from rotating relative to the saddle. 10.The improvement of claim 9, wherein said recess is in communication withpressurized hydraulic fluid and said projection is hollow and opens to abearing surface of said bearing material.